Although it is only a basic prototype, the researchers imagine an amphibious Water Runner robot equipped with biochemical sensors to monitor water quality, deployed with cameras for spying and exploration, or outfitted with bacteria to break down pollutants.

"A legged robot that can walk across land and water literally has the entire world open to it," says Assistant Professor of Engineering Metin Sitti, head of Carnegie Mellon's NanoRobotics Lab. By understanding the mechanics of living creatures such as the gecko lizard, water-strider bugs, beetles, and bacteria, Sitti's research team is building a veritable zoo of fully autonomous, biologically inspired robots that can fly, swim, climb walls, and navigate terrain of all kinds.

"My dream is that, in the end, we will combine all of these forms of dynamic locomotion into one robot," Sitti says. The most recent addition to Sitti's minirobot menagerie mimics the motion of the basilisk lizard, a skittish member of the Iguana family that lives in the rain forests of Central and South America.

In 2004, Harvard University biologists determined how the lizards manage to scamper on the water's surface on their two hind legs, their front arms outstretched, at speeds faster than 1.5 mpsec (about 65 mph). They found that the lizard first slaps the water with its weblike foot, strokes downward with an elliptical motion to create an air pocket, and then pulls its foot out of the water while curling its toes inward.

By repeating this slapping and stroking sequence up to 10 times a second, the lizard generates enough forward thrust and lift to run on water without tipping over or sinking.

With the help of first-year doctoral student Steven Floyd and senior Terence Keegan, Sitti designed a robot with a foot-long, boxy body made from carbon fibers and four plastic legs driven by a lightweight, high-power motor. The legs give the robot the extra lift needed to stay afloat. This stripped-down version of the Water Runner splashes in quick circles around a plastic swimming pool, the first step toward a truly amphibious robot.

"This is proof of concept," says Sitti, who is working with his students to reduce the weight of the robot without hindering its performance.

Once the robot can run smoothly on water, making the transition to land propulsion will be simple, he says. The current generation of Water Runner is tethered to a power supply, but eventually it will be battery-operated and steered by remote control.